The present invention is related to Japanese patent application No. 2000-77831, filed Mar. 15, 2000; the contents of which are incorporated herein by reference.
The present invention relates to a freezing cycle apparatus that uses an evaporator as a radiator for discharged hot gas from a compressor during heating, and more particularly, to a freezing cycle apparatus which uses a variable displacement type compressor.
In the vehicular air conditioner of the prior art, during heating in winter, hot water (e.g., the engine cooling water) is circulated in a heat exchanger for heating, in which the conditioned air is heated with the hot water. When the temperature of the hot water is low, the air blown into the compartment may fail to heat properly. In Unexamined Published Japanese Patent Application No. 11-101514, a freezing cycle apparatus warms with the hot gas heater. Here, when the temperature of the hot water is lower than a predetermined temperature during engine starting, gas refrigerant (or hot gas) discharged from the compressor is introduced into the evaporator while bypassing a condenser to release heat in the evaporator from the gas refrigerant to the conditioned air.
However, in the heating mode of the hot gas heater, the high-low pressure of the freezing cycle rises higher than that of the cooling mode. If the heating ability and the high pressure are controlled by interrupting compressor operation, mechanical shock causes uncomfortable vibrations and reduces durability of the compressor""s electromagnetic clutch. Therefore, the prior art proposed using a variable displacement compressor.
This compressor maintains the evaporator at a predetermined temperature (e.g., 0xc2x0 C.) during cooling. Therefore, if the evaporator temperature rises, the displacement is enlarged to lower the intake pressure. If the evaporator temperature drops, the displacement is reduced to increase suction pressure.
During the heating mode, the evaporator temperature is raised by rising the discharge pressure to augment the heating ability. Therefore, the displacement must be reduced by raising the discharge pressure, and the displacement has to be augmented by lowering the discharge pressure.
Thus, displacement control during cooling and heating must be different. Therefore, a displacement control valve mechanism and the cooling/heating switching valve mechanism are added to the displacement control valve mechanism for the cooling mode with the ordinary variable displacement compressor. The addition, these two valve mechanisms inevitably raises the cost of the variable displacement type compressor.
To address these and other drawbacks, the present invention provides a freezing cycle apparatus with a hot gas heater function, where cooling and heating are correlated to the flow rate of refrigerant circulating in the cycle. During the freezing cycle, moreover, there is a portion where refrigerant flows both during heating and cooling. In this portion, the refrigerant flow rate is detected by a flow rate detecting means shared for cooling and heating operations.
In one aspect of the invention, a freezing cycle apparatus is provided that switches between a cooling mode and a heating mode, where low-pressure refrigerant is evaporated in an evaporator for cooling air and hot gas refrigerant is introduced from the discharge side of a compressor directly into said evaporator to release heat in said evaporator. The apparatus uses a variable displacement type compressor. The displacement of the compressor is controlled such that the refrigerant flow rate in the cycle has a predetermined target flow rate during cooling and heating.
Accordingly, the compressor displacement may be controlled to set the predetermined target refrigerant flow rate during cooling or heating. Therefore, the displacement can be controlled by the control mechanism shared between the cooling and heating modes.
In another aspect of the invention, target flow rate determining means determines target flow rates during heating and cooling modes. Flow rate detecting means detects the refrigerant flow rates during heating and cooling modes. A displacement control means controls the displacement of said compressor so that the refrigerant flow rate, as detected by said flow rate detecting means, may be said target flow rate.
In another aspect, a valve means switches the refrigerant passages such that the gas refrigerant on the discharge side of said compressor is introduced directly to the side of said evaporator in said heating mode and to the side of a condenser in said cooling mode. The flow rate detecting means is arranged between the discharge side of said compressor and said valve means. Then, the refrigerant flow rate on the discharge side of the compressor can be detected by the flow rate detecting means shared between heating and cooling modes.
In another aspect, the flow rate detecting means includes a throttle portion arranged on the discharge side of said compressor, differential pressure detecting means that detects the differential pressure across said throttle portion, and flow rate calculation means that calculates the refrigerant flow rate based on the detected differential pressure.
As a result, the refrigerant flow rate can be calculated based on the differential pressure across the throttle on the discharge side of the compressor. Especially, the throttle portion is arranged on the compressor discharge side, so that the differential pressure necessary for the flow rate calculation can be achieved even if the throttling of the passage is smaller than where the throttle portion is on the cycle lower pressure side.
In another aspect, said predetermined target flow rate is determined such that the temperature of said evaporator is the target temperature.
Accordingly, cooling is controlled by controlling the displacement of the compressor so that the temperature of the evaporator is the target temperature during the cooling mode.
In another aspect, during said heating mode, said predetermined target flow rate is determined such that the cycle high pressure is the target pressure. As such, the heating ability can be controlled by controlling the displacement of the compressor so that the cycle high pressure is the target pressure during the heating mode.
In another aspect, the variable displacement compressor includes a displacement control mechanism and has a throttle portion disposed on the discharge side of said compressor; a differential pressure responding mechanism portion disposed in said displacement control mechanism for varying the displacement of said compressor according to the differential pressure across said throttle portion and the target differential pressure; a target differential pressure setting portion disposed in said displacement control mechanism for setting said target differential pressure by establishing a force against the differential pressure across said throttle portion; cooling time target differential pressure determining means for determining said target differential pressure at said cooling mode by varying the force against the differential pressure across said throttle portion; and heating time target differential pressure determining means for determining said target differential pressure at said heating mode by varying the force against the differential pressure across said throttle portion.
As a result, the compressor displacement can be varied directly mechanically according to the differential pressure across the throttle portion on the compressor discharge side and the target differential pressure by the differential pressure responding mechanical portion of the displacement control mechanism. The differential pressure across the throttle portion on the compressor discharge side varies corresponding to the refrigerant flow rate so that the refrigerant flow rate can be controlled by the displacement control according to the differential pressure change. The displacement is mechanically varied directly in response to the differential pressure change. Moreover, it is possible to improve the responsiveness of the displacement control to the change in the compressor speed.
Since the target differential pressures corresponding to cooling and heating are determined, respectively, by the cooling time target differential pressure determining means and the heating time target differential pressure determining means. Moreover, the compressor displacement can be controlled to achieve the abilities (or the refrigerant flow rates) necessary for cooling and heating. Therefore, it is sufficient to provide the displacement control mechanism shared for cooling and heating. In another aspect, the throttle portion is built in said compressor. In another aspect, during the cooling mode, said target differential pressure is determined such that the temperature of said evaporator is the target temperature. As a result, the displacement of the compressor is controlled to control the temperature of the evaporator to the target temperature during the cooling mode.
In another aspect, during said heating mode, said target differential pressure is determined such that the cycle high pressure is the target pressure. As a result, the displacement of the compressor is controlled to control the cycle high pressure to the target pressure during the heating mode.
In another aspect, the target temperature of said evaporator is varied according to the information indicating the cooling load. Then, the target temperature of the evaporator can be lowered by augmenting the cooling load and raised by reducing the cooling load.
In another aspect, the target pressure of said cycle high pressure is varied according to the heating load. Then, the target pressure of the cycle high pressure can be raised by augmenting the heating load and lowered by reducing the heating load.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In the drawings: